Zeolitic catalysts have found application in many hydrocarbon conversion processes, such as hydrocracking, isomerization and oligomerization. An example of such a process is the oligomerization of an olefinic hydrocarbon-containing feedstock in the presence of a mordenite type catalyst loaded with transition metal ions, such as nickel ions. The use of such catalysts is described in European Patent Application No. 233382. While it is acknowledged therein that the metal-containing mordenite catalyst may be prepared by incorporating the metal ions by any suitable ion exchange method, in practice such catalysts have been prepared by treating the mordenite-type carrier material, which contains exchangeable cations, e.g. ammonium ions, with a solution of a salt of the desired metal under neutral to basic conditions, for example using nickel acetate. While this ion exchange route undoubtedly leads to the preparation of a satisfactory catalyst for the oligomerization of lower olefins, the concentrated solutions of nickel acetate required for the preparation are difficult to handle and, in particular, are unstable and flocculate on standing. However, attempts to use an acidic solution, of nickel nitrate, for introduction of the nickel to the mordenite proved unsuccessful in that poor metal loading was achieved and the resulting catalyst had lower stability than the catalyst prepared by the acetate route.
Surprisingly, we have found that it is possible to prepare such catalysts with adequate metal loading using an acidic metal solution and thus overcome the problems associated with materials such as nickel acetate. Even more surprisingly, we have found that it is possible to prepare such catalysts having a mordenite base, with enhanced activity in the oligomerization of olefins.